The prevalence of type 2 diabetes, impaired glucose tolerance and associated risk factors were compared in sample surveys in Africa and the Caribbean with the Third National Health and Nutrition Survey (NHANES-III) from the United States. A total of 856 Nigerians, 1286 Jamaicans, and 1827 US blacks were included in the study. Body mass index (BMI) increased in a stepwise fashion across the three populations groups, ie, 23 kg/m2 in Nigerians, 26 kg/m2 in Jamaicans, and 28 kg/m2 in US blacks. The corresponding age-adjusted prevalences of type 2 diabetes among persons aged 25-74, were 1%, 12%, 13%. Jamaican women were found to have the same prevalence of type 2 diabetes as US women (14 vs 13%, respectively); mean BMI was likewise very similar (28 kg/m2 in Jamaican and 29 kg/m2 in US women). BMI and waist-to-hip ratio were both associated with type 2 diabetes prevalence. Findings of this study confirm the marked gradient in type 2 diabetes risk among these genetically related populations and suggest that the blacks in the island nations of the Caribbean and the United States are at particularly high risk. Nigerians exhibited remarkably well-preserved glucose tolerance. Understanding the factors that limit the risk of type 2 diabetes in West Africa, beyond relative absence of obesity, would have considerable public health significance.